The present invention relates generally to open-end spinning devices equipped with a spinning rotor.
Spinning units are known in connection with open-end rotor spinning machines in which units the spinning rotor is supported for high speed rotation by its rotor shaft in the bearing slot of a support-disk arrangement and is fixed via a mechanical thrust bearing arranged on one end. The support-disk arrangement has two support-disk pairs mounted on shafts which are angled relative to one another such that an axial thrust is exerted on the rotor shaft to hold the rotor shaft in contact with the mechanical thrust bearing. This type of bearing for open-end spinning rotors is described for example in German Patent Publication DE-OS 25 14 734, and has been shown to operate effectively in practice at rotor speeds of greater than 100,000 rpms.
However, this type of spinning-rotor bearing has the disadvantage that increased friction occurs between the peripheral bearing surfaces of the support disks and the rotor shaft on account of the angled relationship of the support disks, which results in a heating of the contact surfaces of the support disks. Not only are the contact surfaces of the support disks considerably stressed by this frictional heat but additional energy is also necessary to overcome this friction. Moreover, the mechanical thrust bearings are subjected to a not inconsiderable wear, even if properly lubricated.
Therefore, attempts have already be made in the past to replace these mechanical thrust bearings by wear-free thrust bearings, e.g. pneumatic bearings or magnetic bearings. Since an axial thrust of the rotor shaft in the direction of the thrust bearing is also required in the case of pneumatic bearings, most of the above-discussed basic problems are not able to be eliminated with pneumatic bearings.
German Patent Publication DE 195 42 079 A1 describes an axial magnetic-bearing arrangement in which a part of the magnetic bearing elements are arranged stationarily in the housing of a thrust bearing and the other part of the magnetic bearing elements are arranged in a detachable manner on the rotor shaft of the spinning rotor. Various embodiments are suggested regarding the connection of the magnetic bearing elements rotating with the spinning rotor to the rotor shaft.
A few of these variants concerns a non-positive fastening and others a positive fastening of the rotating magnetic bearing elements, which can be readily detached if necessary. A correct axial fixing of the rotor shaft on the support-disk bearing arrangement is possible with these known magnetic bearing devices and it is also assured that the spinning rotor can be smoothly mounted and dismounted if necessary. However, while the non-positive, easily detachable fastening of the magnetic bearing component to the rotor shaft is advantageous in principle, this type of bearing device is still in need of improvement. A particular problem in such magnetic bearing devices is the fastening of the rotating magnetic bearing elements to the rotor shaft since substantial requirements are placed on the balance quality of this connection on account of the high speed of the spinning rotor.
An open-end rotor spinning device with a permanent magnetic thrust bearing is also known from Austrian Patent 270,459. In this bearing arrangement, ferromagnetic annular attachments are arranged on the end of the rotor shaft of a spinning rotor and are opposed by pole elements of a permanent magnet pivotably supported in this area. The bundling of the magnetic lines of force of the permanent magnet achievable by such an arrangement results in a relatively stiff fixing of the rotor shaft in the bearing nip of a support-disk bearing. However, a magnetic bearing arrangement designed in this manner has the disadvantage that the annular attachments arranged on the rotor shaft have a distinctly greater diameter than the rotor shaft itself. Since these larger annular attachments may prevent the mounting and dismounting of the spinning rotor, especially its front-side mounting, or at least make this operation considerably more difficult, this known magnetic bearing arrangement has not been accepted in practice.
German Patent Publication DE 30 47 606 A1 teaches a bearing for a spindle of a textile machine which rotates at a relatively high speed. The spindle is supported in the radial direction via a three-point bearing arrangement similar to a support-disk bearing and is secured in the axial direction by a magnetic bearing. One end of the spindle comprises a bearing area stepped in its diameter with two ferromagnetic annular attachments. A muff manufactured from a non-magnetic material is fixed to the bearing housing as a stationary bearing element and an annular permanent-magnet element enclosed by lateral pole disks is fitted into which muff. In the mounted state of the spindle the ferromagnetic annular attachments of the spindle shaft stand opposite the pole disks of the permanent-magnet element fixed in the stationary bearing element. Even though this known design makes possible a relatively smooth mounting and dismounting of the spindle in an axial direction, the device has not been accepted in practice on account of its deficient axial bearing stiffness.